Drying method



March 2, 1943. 'D. D. PEEBLES DRYING METHOD Fild Oct. 10, 19:59

2 Sheets-Sheet l l I R INVENTOR flaw/'0 fl. eeb/es BY Z ATTORN EY March 2, 1943. D- PEEBLES 2,312,474

DRYING METHOD 7 Filed Oct. 10, 1959 2 Shets-Sheet 2 INVENTOR ATTORNEY Patented Mar. 2, 1943 DRYING METHOD David D. Peebles, Berkeley, Califl, assignor to Golden State Company, Ltd., San Francisco, Calif., a corporation of Delaware Application October 10, 1939, Serial No. 298,795 1 12 Claims. (Cl. 159-48) This invention relates generally to methods for converting various materials in liquid form to dry, powdered products. It is particularly applicable to materials containing protein susceptlble to coagulation by heating, as for example skim milk or like milk products. 4

In the manufacture of dried milk products, as for example powdered skim milk, it is customary practice to make use of spray drying equipment such as equipment of the Gray-Jensen type (see Hunzickers Condensed Milk and Milk Powder, published 1934, 5th edition). While installations of such equipment give satisfactory results within the limits of capacity for which they were originally designed, attempts to operate at an increased capacity, as for example by increasing the percentage ofsolids in the material supplied to the spray drying chamber and by increasing the exhaust temperature-of the drying gas, result izra dried material of seriously impaired quality. Solubility of the material is impaired, and there is a noticeable tendency toward discoloration. I have found that the impairment in solubility is due to increased coagulation of milk proteins,

which are known to be susceptible to coagulation V by heating.

The present invention has for its object the provision of an apparatus and method capable of operation at relatively high capacity for a given size ofspray drying chamber with the production of a high quality product. The invention is characterized by the use of a pluralityof drying zones in which the material being dried is suspended in drying gas, with the drying being carried out in two or more stages in such manner as to avoid coagulation of milk protein or impairment of color.

Further objects of the invention will appear from the iollowing description in which the preferred embodiments have beenset forth in de- 2311 in conjunction with the accompanying draw- Referring to the drawings Fig. 1 illustrates diagrammatically apparatus for carrying out the present invention.

Fig. 2 illustrates another form on apparatus for carrying out the invention.

Fig.3 is a detail illustrating the construction of a portion of the equipment shown in Fig. 2.

the discharge side of the blower through the conduit II into the upper portion of the drying chamber I2. The heater 13 serve to elevate the ,ment of the atomized particle in the gas.

temperature of the drying gas to the temperature level desired. Gas is discharged from chamber l2 through conduit 54. The liquid material being desiccated is introduced through pipe l6, and atomized by the spray nozzle I'I. known to those skilled in the art, the hot drying gas is introduced tangentially intothe desiccat-' ing chamber, whereby the gas within-the cham-,

ber swirls about a vertical axis, with entrain- In the ordinary use of such apparatus the lower conical end of the drying chamber is connected to a conduit for the removal of the dried material.

In carrying out the present invention, the material delivered into the spray drying apparatus it is treated in additional apparatus for further removal of moisture content. Also, the initial drying step carried out by the spray drier l0 is'operated at a greatly increased capacity and in such a manner that the material is convertedto solid form short of complete moisture removal, and without substantial coagulation of milk protein.

- Treatment by the additional apparatus subjects the material to the action of a drying as in one or more additional drying zones, to efi'ect rapid removal of remaining moisture without coagulation of proteins or impairment of color.

Referring again to Fig. i, the lower end of the chamber 82 is shown connected to a conduit l8, which in turn connects to a secondarydrying chamber l9. The inlet end ofconduit I8 is supplied with hot gas from a suitable source, as for example by way of conduit 20 which leads to the discharge side of heater i3, 01 by way of a supplemental air heater 2i. Gas is withdrawn from chamber 99 through conduit 22 and delivered by blower 23 to the classifying apparatus 24., Conduit 26 withdraws the classified material and delivers it to a cyclone separator 21. Blower 28 withdraws the material from separator 21 and delivers it to another cyclone 29. The collected material from cyclone 29 can be withdrawn into a collecting hopper 3 i, and passed through a sliting apparatus 32 to form a final finished material.

While the form of the drying chamber l9 may vary, in this instance it is a relatively simple cylindrical shaped chamber having conduit l8 connected tangentially through one side wall, whereby gaseous material within the chamber swirls about the central axis at relatively high veloci ties. Classifier 24 can be formed'generally as in-- dicated, with an internal baiile wall 33 interposed As is well 7 accomplished by the fact that that portion of tion to the extent of from say 30 to 50% solids,

, of the moist material withdrawn from chamber I 2 across the region of the outlet opening. Coarser material discharged by blower 23 impacts with baflle 33, whereby such material is prevented from passing out through conduit 26 with the finer sized material. In time impacting of the coarser material upon baiile 33 breaks this material into finer particles for discharge.

In carrying out the present method by use of the apparatus shown in Fig. 1, gas delivered into the chamber I9 together with the material withdrawn from chamber I 2 must have a relative humidity substantially less than the relative humidity of the gas being withdrawn from the desiccat in'g chamber I2. In the present instance, this is the gas withdrawn from the desiccating chamber 12 together with the particles of partially dried material, is intermixed in conduit l8 with hot drying gas of low relative humidity supplied through conduit or heater 2|. Within chamber-l9 H further evaporation takes place at a rapid rate to convert the material to an anhydrous product, and the drying within this chamber takes place under such conditions that milk proteins are not coagulated to any substantial degree, nor the color impaired. a a By way of example, the gas, upon leaving th heater l3 and as introduced into the desiccating chamber l2, may be at a temperature of about 260 Fahrenheit. The temperature at which the moist gas is exhausted from chamber l2 through conduit H can be about 170 Fahrenheit; That portion of the gas being withdrawn from the lower end of chamber [2 together with the material being dried will be at substantially the same temperature as the gas discharged from conduit l4, that is about 170 Fahrenheit. Hot gas supplied to conduit l8 by way of conduit 20 or heater 2| can be about 220 Fahrenheit. For the temperatures of operation specified, the temperature of .the gas leaving classifier 24 will be about 150 Fahrenheit, and should not be saturated with moisture. The moisture content of the material withdrawn from the desiccating chamber l2can range from about-4 to 10%, while that of the finished product'may range from 0.5 to 3%, as desired.

r A particular feature of my method is that a spray drying apparatus H of a given size can be operated at relatively high capacity, with production of a high quality product. In this connection it maybe noted that equipment of the -G ray-Jense'n type as operated in the past is supplied with a concentrated material such as skim milk. whereas the present process makes possible tkim'milk, the milk isiconcentrated by evaporaabout 35% being customary, whereby the effective capacityof the spray drier is greatly increased. when operating at high capacity according to the present method, the protein content is not'coagulated, since all of the drying takes place at a rapid rate. p

. Inlthe secondary chamber l9, conditions are such as to promote further moisture removal-at a relatively rapid rate, because of the low-relative humidity of the gas, and also because there is 7 more turbulence and higher velocities of gas flow better contact within. chamber i9 than in chamber i2. Rapid moisture removalprevents any substantialv degree of protein coagulatiom since evaporation of moisture from the particles 76 keeps the particles within a temperature range at. which little if any coagulation takes place,

while at thesame time producing a relatively ,anhydrous product. The removal of the final moisture protects the particles against the heat of the drying gas, whereby this stage of the-drying is carried out without substantial coagulation of the milk protein.

. In the embodiment of Fig. 2 the secondary drying and classification 6f the material is carried out l by the use of a single piece of equipment. Blower 3B is shown receiving material from desiccating chamber I2, together with the desired proportion of exhaust gas, and this material is delivered to the cyclone separator 31. From the cyclone 31 the material is delivered to conduit 33 which connects tangentially with a secondary drying chamber 39. Conduit "receives hot dry gas from the. heater 4|. Chamber 39 also connects with conduits 42 and 43, which together with the external blower 44, form a recirculating path for gas and material being dried. Conduit l6 withdraws gas and dried material from chamber 39 and is shown connected to blower 41, which in turn connects with the cyclone separator 48 and collecting hopper 49. v

Chamber 39 is preferably cylindrical or circular in contour andto afford a classifying action, its interior is provided with the annular shelves 5| and 52. Conduit 33 connects with the chamber ata level between these shelves, while the return conduit 43 connects tangentially above the shelf ii. The point of connection 7 of conduit 46 through the top wall of the chamher is offset laterally from the' central axis. Conduit 53 connects at ,a level above shelf 3| and can be used'to intermittently or continuously bleed off material collecting above this s it, by controlling valves or damper ll.

In general, the apparatus of Fig. 2 operates as described above for Fig. 1. Cyclone separator 31 serves to exhaust some of the moist warm air withdrawn with the material from desiccating chamber, l2. Upon leaving the'separator 31 the material is entrained with the hot drying gas fromheater 3|, and delivered with this dry gas into the chamber 33. Within chamber .33 the materialis entrained by the swirling drying gas and the efiective period of retention of the material with the drying gas ,is' prolonged'by virtue of recirculation through blower. The

shelves II and 32 cause the apparatus-to func- 'tion as a classifier. to effectively retain coarser material with discharge of only the flnermaterial through theconduit 33. The coarser mterial is in time pulverized and likewise 'del'iv ered to conduit 48. l I claim:

1. In a method of heating, the steps o1maintaining'twojaonesot drying gas by continuous introduction of hot gas into and removal ofjgas .fromeach zone,1spraying the material into one zone whereby evolu tlon of moisture converts the material into solid duced into the second zone having a res-met humidity substantiallyless. than that of discharged from the first zone.

- drying liquid material con 0 taining protein susceptible to (coagulation by the 2'. In a method of drying liquid material con-- taining protein susceptible to coagulation by heating, the steps of maintaining at least two zones of drying gas by continuous introduction of hot gas into and removal of gas from each zone, spraying the material into one zone with suspension of the particles in the drying gas whereby evolution of moisture converts the material into moist but solid particles without coagulation of protein, and then causing the particles to progress in a stream of gas without rest into the second zone with suspension of the particles in the gas maintained in said second zone for further removal of moisture content to form an anhydrous product substantially free of combined moisture, the gas introduced into the second zone having a relative humidity substantially less than the relative humidity of the gas discharged from the first zone.

3. In a method of drying liquid material containing protein susceptible to coagulation by heating, the steps of maintaining primary and secondary zones of drying gas by continuous introduction of hot gas into and removal of gas from each zone, spraying the material into the.

primary zone with suspension of the particles in the drying gas whereby evolution of moisture from the particles converts the same into solid form without substantial coagulation of protein, conveying the particles without rest from the primary to the secondary zone with suspension of the particles in the gas maintained in the secondary zone, whereby further moisture re moval occurs in .the secondary zone to convert the material to dry form, the gas introduced into the secondary zone having a relative humidity substantially less than that of the gas discharged from the first zone.

4. In a method of drying milk products like skim milk, concentrating the milk product by evaporation, maintaining a plurality of zones of drying gas by continuous introduction of hot gas into and removal of gas from each zone, spraying the concentrate into one zone whereby evolution of moisture from the particles converts the material into moist but solid particles without coagulation of protein, immediately causing the particles to progress without rest into a subsequent drying zone with suspension of the particles in the gas maintained in said subsequent zone for further rapid removal of moisture content to form an anhydrous material having substantially no combined moisture, the gas introduced into the second zone having a relative humidity substantially less than that of the gas discharged from the first zone.

5. In a method of drying liquid material con- I taining protein susceptible to coagulation by heating, the steps of maintaining a plurality of zones of drying gas by continuous introduction of hot gas into and removal of gas from each zone, spraying the material into one zone whereby material is placed in suspension with the drying gas and whereby evolution of moisture converts the material into moist but solid particles without substantial coagulation of protein, removing the'particles from the first named zone together with a portion of the drying gas, causing the particles to progress without rest fidm said first zone into .a second drying zone with suspension of the particles in the gas maintained in said second zone for further removal of moisture content to form a dry product containing not more than about 3% moisture, the

gas introduced into the second named zone having a relative humidity substantially less than the relative humidity of the gas removed from the first named zone together with the material, and then collecting the dry material. I

6. In a method of drying liquid material containing protein susceptible to coagulation by heating, the steps of maintaining at least two zones of moving drying gasby continuous introduction of hot gas into and removal of gas from each zone, spraying the material into one zone whereby the material is suspended in the drying gas with evolution of moisture to convert the material into moist but solid particles without substantial coagulation of protein, and then causing the particles to progress without rest into the second zone with'suspension of the particles in the gas maintained in said second zone for further'removalof moisture content to form a dry product, the gas introduced into the second zone having a relative humidity substantially less than that of thegas discharged from the first zone, and the velocity of movement of the gas in the second zone being substantially greater than that of the first zone.

'7. In a method for the manufacture of a dry product from a liquid material, containing one or more components susceptible to coagulation by heat, the steps of removing water from the material at a rate sufiicient to keep the material at a temperature below that causing coagulation of said components, by spraying the material into a hot drying gas of low relative humidity, whereby the material is converted to moist but solid divided form, and then transferring the material without rest to a second hot drying zone and suspending the particles of said material in a drying gas in said second zone for'elIecting removal of moisture in the second zone to a value not more than about 3% and at a rate sufficiently rapid to maintain the particles at a temperature below that which causes coagulation of said components.

8. In a method of drying liquid material containing solids, the steps of maintaining at least two zones of drying gas by continuous introduc- 'tion of hot gas into and removal of gas from each zone, the gas in each zone being in continual motion, spraying the material into one zone whereby the material is suspended in the drying gas with evolution of moisture to convert the material into moist but solid particles, and then causing the particles to progress without rest into the. second zone with suspension of the particles in the gas maintained in said second zone for further removal of moisture to form a dry product, the gas introduced into the second zone having a relative humidity substantially less than that of the gas discharged from the first zone, and the velocity of movement of the gas in the second zone being substantially greater than that of the first zone. 9. In a method of drying liquid material containing proteins susceptible to coagulation by heating, the steps of maintaining'primary and secondary zones of drying gas by continuous introduction of hot drying gas into and removal of gas from each zone, spraying the material into the primary zonev with suspension of the particles in the drying gas whereby evolution of moisture from the particles converts the same to solid form without substantial coagulation of protein, conveying the particles in a stream of gas without rest from the primary to the secondary zone, .causing the particles to be suszone, whereby further moisture removal occursin the secondary zone to convert the material I to dry form, the gas introduced into the sectaining protein susceptible to.coagulation by heating, thesteps oi maintaining a plurality of zones of drying gas by continuous introduction of hot gas into and removal of gas from each zone, spraying the material into one zone whereby particles of the material are suspended in the drying gas to cause evolution of moisture where by the material is converted into solid particles without substantial coagulation of protein, causing the solid particles to progress from said one zone into anotherdrying zone for further re-.

moval of moisture content to form a dry product, the gas introduced 4 into the last named zone having irrelative humidity substantially less than that 01' the gas discharged from the first named zone, removing finely divided dry material from the last drying zone, and causing coarser particles of the material in. said last named zone to be reduced to flner particle size for removal by continually agitating and impacting the same.

11. In a method of drying liquid material containing protein susceptible to coagulation by heating, the steps, of maintaining two zones of drying gas by continuous introduction of hot gas into and removal of gas from eaclgfione, spraying the material into'a first drying ne whereby revolution of moisture converts'the material into moist but solid particle's without substantial coagulation of protein. causing the particles to 35 zone.

immediately progress without rest from the first zone to the second zone with suspension of the particles in the gas maintained in the secondary zone for further removal of moisture content to 5 form a dry product, the gas introduced into the second zone having a relative humidity substantially less than that of the gas discharged from the first zone, and continuously recirculating drying gas through the second zone by way oi a circulating path external of the zone to cause a velocity of movement of gas in the second zone which is greater than the velocity of movement of drying gas in the first zone.

12. In a method of drying liquid material containing proteins susceptible to coagulation by heating, the steps of maintaining primary and secondary zones of drying gas by continuous introduction of hot' drying gas into and removal of gas from eachzone, spraying the material into the primary zone with suspension 01 the 1 particles in the drying gas whereby evolution of v moisture from the particles converts the same to solid form without substantial coagulation of protein, conveying the particles in 'a stream of gas without rest from the primary to the secondary zone, causing the particles to be suspended in the gas maintained in the secondary zone, the gas flow in the secondary zone being at higher velocities than in the primary zone,

whereby further rapid moisture removal occurs in the secondary zone to convert the material to dry form, the gas introduced into the secondary zone having a relative humidity substantially less. than that of the gas discharged from the first DAVID n. "PEEBLES. 

